1. Field of the Invention
The present invention relates to a magnetic disc recording and/or reproducing apparatus such as a floppy disc drive unit or the like.
2. Description of the Prior Art
In data recording and/or reproducing apparatus using a floppy disc or the like, high-precision parts or mechanisms are required as the track density is increased. The proportion of the track pitch error to the tracking error factor is one of the most important design factors. If the allowable error of the drive mechanism included in the overall tracking error is relatively large, the precision of the drive mechanism can be low and the overall apparatus can be less expensive. During the design stage, the factors which cause offtrack errors that may be caused during production and which theoretically arise must be completely eliminated.
When concentric tracks are formed on a disc, the track pitch error changes in accordance with the distance from the center of the disc along the radial direction. That is, since the radius of curvature increases toward the center of the disc the track pitch error increases toward the center of the disc. For this reason, the design is generally accomplished such that the tracking error remains within an allowable range so that the worst offtract at the innermost track during reproduction does not occur. However, in a so-called micro floppy disc having a diameter of 3.5 inches, for example, the track pitch error at the innermost track is very large. For this reason, high precision is required for the chucking mechanism for the disc and for the head drive mechanism which results in expensive apparatus.